The present invention relates to processes for treating exhaust gases containing fluorine-containing compounds, particularly to exhaust gas treatment processes and systems capable of efficiently and long treating perfluoro-compounds discharged during the step of dry-cleaning the inner faces or the like of semiconductor manufacturing apparatus with perfluoro-compounds such as C2F6, C3F8, CF4, CHF3, SF6, NF3, etc. or the step of etching various films in the semiconductor industry. In more preferred embodiments, the present invention relates to exhaust gas treatment processes and systems capable of efficiently treating oxidizing gases such as F2, Cl2 and Br2; acidic gases such as HF, HCl, HBr, SiF4, SiCl4, SiBr4 and COF2; and CO in addition to the perfluoro-compounds.
In the semiconductor industry, many kinds of noxious gases are used during semiconductor manufacturing processes, which raises concerns about environmental pollution. Perfluoro-compounds (PFCs) contained in exhaust gases from etching processes or CVD processes are global warming gases for which a removal system should be urgently established.
PFC removal processes have been proposed such as destruction and recovery techniques, especially destruction techniques including various catalytic pyrolysis methods. For example, proposed prior processes include an exhaust gas treatment process using an alumina-based catalyst loaded with various metals; an exhaust gas treatment process using alumina containing 0.1% by weight or less of Na as metal; an exhaust gas treatment process involving contacting exhaust gases with molecular oxygen in the presence of alumina; a process for treating exhaust gases containing fluorine-containing compounds using an Al-containing catalyst in the presence of water vapor at a temperature of 200-800xc2x0 C.; a process for treating exhaust gases containing fluorine-containing compounds using various metal catalysts in the presence of molecular oxygen and water; etc.
However, these prior proposals had the problems that fluorine-containing compounds were decomposed with still too low efficiency to obtain sufficient treatment performance or a long continuous treatment could not be attained with a given treatment system because of the short life of the alumina catalysts.
Thus, an object of the present invention is to solve these problems of the prior art and to provide a process and a system for treating exhaust gases containing fluorine-containing compounds with high PFC decomposition efficiency, which allows PFCs to be effectively decomposed and eliminated for a long period.
As a result of careful studies to solve the above problems, we found that the above object can be achieved by using an alumina having a specific crystal structure among those having various crystal structures. Accordingly, the present invention relates to a process for treating an exhaust gas containing a fluorine-containing compound with a catalyst, characterized in that said catalyst is a xcex3-alumina having a crystal structure showing diffraction lines having an intensity of 100 or more at the following five diffraction angles 2xcex8: 33xc2x0xc2x11xc2x0, 37xc2x0xc2x11xc2x0, 40xc2x0xc2x11xc2x0, 46xc2x0xc2x11xc2x0 and 67xc2x0xc2x11xc2x0 measured by an X-ray diffractometer.